Ok Looking like it is definately ECU and dealer not trying to make a quick buck, they have said that if it is not the ECU they won't charge me a penny, I'll get that in writing.
Lets see what MB customer services do by way of contribution and if all else fails we'll see what Warranty Direct say (I'm sure it's covered) Will still cost me a bob or two as Parts are only covered 70% and labour £40hr